18.1. SPI Overview

When you implement a new Presto plugin, you implement interfaces and override methods defined by the SPI.

Plugins can provide additional connectors, types, functions, and system access control (see Connectors, Type System, Functions, and System Access Control respectively). Connectors in particular are the source of all data for queries in Presto: they back each catalog available to Presto.

Code

The SPI source can be found in the presto-spi directory in the root of the Presto source tree.

Plugin Metadata

Each plugin identifies an entry point: an implementation of the Plugin interface. This class name is provided to Presto via the standard Java ServiceLoader interface: the classpath contains a resource file named com.facebook.presto.spi.Plugin in the META-INF/services directory. The content of this file is a single line listing the name of the plugin class:

com.facebook.presto.example.ExamplePlugin

For a built-in plugin that is included in the Presto source code, this resource file is created whenever the pom.xml file of a plugin contains the following line:

<packaging>presto-plugin</packaging>

Plugin

The Plugin interface is a good starting place for developers looking to understand the Presto SPI. It contains access methods to retrieve various classes that a Plugin can provide. For example, the getConnectorFactories() method is a top-level function that Presto calls to retrieve a ConnectorFactory when Presto is ready to create an instance of a connector to back a catalog. There are similar methods for Type, ParametricType, Function, SystemAccessControl, and EventListenerFactory objects.

Building Plugins via Maven

Plugins depend on the SPI from Presto:

<dependency>
    <groupId>com.facebook.presto</groupId>
    <artifactId>presto-spi</artifactId>
    <scope>provided</scope>
</dependency>

The plugin uses the Maven provided scope because Presto provides the classes from the SPI at runtime and thus the plugin should not include them in the plugin assembly.

There are a few other dependencies that are provided by Presto such as javax.inject and Jackson. In particular, Jackson is used for serializing handles and thus plugins must use the version provided by Presto.

All other dependencies are based on what the plugin needs for its own implementation. Plugins are loaded in a separate class loader to provide isolation and to allow plugins to use a different version of a library that Presto uses internally.

For an example pom.xml file, see the example HTTP connector in the presto-example-http directory in the root of the Presto source tree.

Adding a custom Plugin to Presto

In order to add a custom plugin to Presto, create a directory for that plugin in the Presto plugin directory. Then, add all the necessary jars for the plugin to that directory. For example, for a plugin called my-functions, you would create a directory my-functions in the Presto plugin directory and add the relevant jars to that directory. By default, the plugin directory is the plugin directory relative to the directory in which Presto is installed, but it is configurable by the configuration variable plugin.config-dir. In order for Presto to pick up the new plugin, you must restart Presto.